The present invention relates to the field of cartography and more particularly to a method and a device for annotating electronic background maps adapted in particular to navigation aid devices for vehicles.
Traditionally, aircraft crews and the ground preparation staff use paper maps on which annotations are made in handwriting. Such annotations relate, for example, to flight indications, especially of highways or of air corridors, as well as to tactical information items in the case of military flights.
FIG. 1 illustrates an example of an annotated paper map 100 formed from a background map 105 and annotations 110.
Furthermore, there exist electronic navigation aid devices making it possible to display electronic background maps.
Two formats typically exist for electronically representing a map. A first format corresponds to a paper photograph of the maps, and moreover it often relates to paper maps that have been digitized. According to this format, the electronic map can be considered as an image or as a matrix whose abscissas and ordinates represent geographic coordinates, in latitude and longitude, for example, and whose value represents a color, or in other words an information item about the nature of the point, such as a topological indication. The indications given by the map, such as a place name, are represented in the same way, by a set of color points. Electronic maps using this format are generally known as raster maps in English terminology.
According to a second format, a description of the map is used to generate the map or a part of the map when this is used. Such a description comprises a geometric description of elements of the map. Thus, unlike the first format, a highway is characterized not by a set of points of the same color but by a set of geometric elements such as vectors and circular arcs. The indications given by the map are also represented in descriptive form, for example in the form of lists comprising pairs of geographic position and character strings. The electronic maps using this format are generally known as vector maps.
An advantage of vector maps over raster maps lies in the density of information items that can be stored in memory, or in other words in the number of information items that can be stored in memory for a given storage capacity, as well as in the simplicity of certain processing operations, such as the choice of density of viewed information items.
The raster maps are generally obtained directly from existing paper maps. They are determined for a given scale. For example, 1:50,000 and 1:250,000 maps exist. The choice of scale is determined by the density of desired information items.
Furthermore, the raster maps are recorded with a precision defined during digitization. Thus it is possible to determine the resolution of each map point, also known as pixel (acronym for Picture Element in English terminology), or in other words the length represented by this point. The resolution of a pixel is the ratio of the map scale to the resolution of the digitization. When a raster map is displayed on a screen, it is possible to change the viewing scale by using standard image-processing functions such as interpolation.
Navigation aid devices are generally centralized devices adapted to select the map to be displayed, typically a map of raster type, and to determine the display resolution and the position of the map relative to the screen. The selected map can be displayed in real time on a navigation screen, thus forming a background map on which supplementary information items can be displayed by superposition. Such supplementary information items are, for example, points of interest, known as waypoints in English terminology. All of the calculations necessary for addition of these information items are often implemented in the navigation aid devices.
However, although the navigation aid devices furnish useful information items to the users in real time, they do not permit manual annotation of the displayed background maps.